This invention relates to a method for controlling operating parameters in a precious metal recovery operation involving froth flotation and optionally cyanidation.
Froth flotation is widely used for recovering mineral value. It generally involves the use of gas injection including, for example, air, through a slurry that contains water, minerals and gangue particles within a vessel. Minerals are separated from gangue particles by taking advantage of their differences in hydrophobicity. These differences can occur naturally, or can be controlled by the addition of a collector reagent in conjunction with pH control.
Mineral separation using froth flotation is typically achieved via several flotation stages, defined as rougher stage, scavenger stage and cleaners stage. During these several stages, the economical product grade, called concentrate grade, is gradually improved to eventually yield a concentrate of acceptable grade to be sold to a smelter. Each flotation stage produces tails, a secondary product that, for intermediate stages, is frequently recirculated back to the flotation step behind. This recirculating configuration is called a closed circuit flotation configuration. The final tails in a closed circuit process are the scavenger tails. In an open circuit process, some cleaner tails are commingled with the final scavenger tails. Mineral recovery and concentrate grade are important factors in the operation of a successful froth flotation plant.
It has been the practice in froth flotation operations to utilize rather fixed targets for concentrate grade and mineral recovery. Those targets are usually based on flotation performance characterization, ore composition, experience and economical criteria. The fixed targets typically represent an operating range for the flotation circuit, but do not necessarily reflect the best economical performance of the plant in a real-time fashion if the characteristics of the specific minerals being floated are not taken into account.
Heretofore the concentrate grade and mineral recovery targets have not necessarily been variable or accounted for real-time occurring mineralogy, refractory ores occurrences, head grade variation and metal prices. Prior processes have used a net smelter return (NSR) generated from the concentrate grade, metal recovery, flotation reagent costs and other economical parameters to monitor performance. Net smelter return has been implemented through a strategy that includes theoretical grade-recovery curves or other types of metallurgical models. Such models usually have fixed parameters which do not present significant adaptability and flexibility. Consequently, such models do not provide real-time control in relation to the several variables mentioned above. One such prior proposal was disclosed by Bazin et al., "Tuning Flotation Circuit Operation as a Function of Metal Prices," Conf. Mineral Proc. 1997.
Cyanidation is sometimes employed in conjunction with flotation to recover gold values from flotation tails. Tails are contacted with cyanide in a series of agitated tanks to dissolve gold particles, producing a solid phase having a minimum gold content and a liquid phase having a maximum gold content. The gold is then recoverable by conventional means, such as the Merrill-Crowe process or others.
During cyanidation, minerals known as cyanicide minerals release into solution other elements including arsenic, iron, copper, sulphur and others along with gold. Copper solubilization, for example, can range from about 5% with chalcopyrite to about 95% with azurite. Cyanicide minerals are problematic because they consume cyanide, thus increasing reagent costs. Copper, for example, consumes 2 to 4 moles cyanide per mole copper, thus increasing costs by up to as much as several dollars per tonne of ore treated. High cyanide consumption also requires expensive detoxification of the final leached plant residues.
As two or more copper minerals and other cyanicide minerals are present in an ore body, processing becomes more complex. The complexity arises from the fact that cyanide consumption varies widely and cyanide demand for adequate gold recovery varies widely. Furthermore, detoxification reagent consumption varies widely. Where demand for cyanide and detoxification reagents are great, or vary greatly, optimum economical operation does not necessarily correspond to optimum metallurgical performance in terms of metal recovery.